The studies embody three specific and related purposes, each designed to further evaluate the validity of our linguistic deficit explanation of reading disability. The first is to provide edification of our suggestion that severely impaired readers have particular difficulty in encoding what we have termed the structural or "purely linguistic" attributes of spoken and written words, that is, their phonological, syntactic and grammatical attributes. A second purpose is to conduct a major training study to evaluate the relative contributions of various subskills to performance on a new learning task simulating word identification. The third purpose is to extend our inquiry to include a wider range of reading ability levels in the interest of determining whether test profiles on critical measures would be similar in respective groups, or would differ in ways that might conform with etiologically distinct subtypes. Eight studies have been proposed. Six small scale studies will contrast severely impaired and normal readers on various aspects of linguistic processing. One study will compare these reader groups on differential sensitivity to root and bound morphemes in spoken language, and a second will compare them on differential sensitivity to phonological and orthographic codes in spoken language. A third study will evaluate the extent to which fast and slow rates of stimulus presentation interact with immediate and delayed recall as determinants of reader group differences in verbal memory. Two others will compare these two groups on their ability to encode consonants and vowels in spoken language, and another will compare them on categorical perception of these two types of phonemes. The two remaining studies are large scale studies. The first will evaluate the relative contribution of reader group and individual differences in visual memory, alphabetic mapping ability and lexical memory to performance on a simulated word identification task with and without the influence of training in alphabetic mapping and lexical enrichment. The final study contrasts severely impaired, moderately impaired, average and good readers on a variety of measures of cognitive and linguistic ability and reading subskills in order to evaluate whether etiologically distinct subgroups exist exclusively among reading impaired populations.